Whether we transmit an electrical signal over copper wires, or an optical signal over fiber optics, or a radio signal over the radio, or just shout across an open field, the information degrades with distance and time. It gets harder to hear the signal over the noise. The signal gets weaker with distance. So the trick is to find ways to keep the signal intact for as far as possible. We also want the receiver (or listener) to be close enough that the signal is still clear even if there's noise around. For example, if I can't hear you shout across a tree-filled forest, I could use an amplifier to make my voice louder, or I could cut down the trees, or both. Similarly, if I want to transmit information using pulses of light in an optical fiber, I can either use an amplifier to make the light brighter, or I can make the glass fiber extremely pure and smooth so the light doesn't get absorbed or scattered along the way. Then the signal will travel a longer distance before it gets lost in the noise.

There's also an effect called dispersion, which makes high frequencies travel at a different speed than low frequencies. Another kind of dispersion acts like a kind of echo-filled hallway, so your "words" arrive at different times. Both of these types of dispersion will garble the message, and they get worse with distance. So we try to design both copper cables and optical fibers (glass fibers) to minimize dispersion. Or we just use them for short distances where dispersion doesn't matter.

It can't, technically, but the transfer of information comes in a series of on-and-off signals (in copper) or light (in glass). You do lose energy, and thus information, along the way. You can basically think of information traveling by way of electrical current as an extremely complicated form of Morse Code. Glass is a little more complicated, but it's the same principle.

That's a great question! When engineers were trying to figure out how to send information from one place to another, they often wondered this exact same thing. If you ever used a television with an analog antenna, you probably saw the screen get fuzzy at certain times. This is due to lost information - the very information you're asking about, in fact.

In order to get around this lost information, we broadcast most information over a digital signal nowadays. Digital signals only have two possible results, 0 or 1. In this way, it's really easy to keep track of what the original information is. If we're only expecting to see a 0 or a 1, and we see a signal that says "0.837", we can be pretty sure this is still close enough to 1 to call it a 1. This way, the signal can still degrade, but information isn't lost.

It's actually a bit more complicated than this, and there are many engineers who are still designing tricks to figure out whether an actual error has been made (a 0 switched to a 1, for example).